My invention relates to an electrode, particularly an ultramicroelectrode, a process for its manufacture and its use or applications.
An ultramicroelectrode with a conductor made of noble metal wire or carbon wire with an insulating layer located on it is known.
Ultramicroelectrodes are made from very thin electric conductors in the form of filaments or wires with a diameter of a few micrometers and an insulating layer located on it. It is required of these electrodes that they be useable in a wide range of solvents, simple to build, have exact measured dimensions and can produce reproducible results.
The insulating layer of the ultramicroelectrode used currently is made of glass or an epoxy resin. Such microelectrodes are described in the following literature references:
R. W. Wightman and D. O. Wipt, Electroanalytical Chemistry, Vol. 15, pp. 44 to 51, New York, Marcel Dekker-Verlag(1970), Martin Fleischmann, Stanely Pons, Debra R. Rolison and Parbury P. Schmidt: Ultramicroelectrodes, Kapitel 3, pp. 66 to 106, Datatech Systems, Inc., Science Publishers, (1987); D. W. Hill, B. W. Watson, IEE Medical Electronics Monograph 7-12, I. Microelectrodes and Input Amplifiers, pp. 1 to 26, Peter Peregrinus Ltd. (1974). Conventional ultramicroelectrodes are made in the following way: One draws a glass tube into a capillary and in the capillary so drawn introduces a wire or a filament made of noble metal and/or carbon. Then the wire is heat sealed in the glass tube. The thickness of the insulating layer made of glass or epoxy resin is approximately about 1 to 2 mm. Building a uniform layer thickness over the entire electrode length is difficult.
Ultramicroelectrodes with glass insulation are very fragile, since hair-line fractures occur in glass because of thermal stress caused by the difference in the thermal expansion coefficient of glass and the filament material. The hair-line fractures are the basis for a comparatively strong increase in the electrode surface area, for nonlinear diffusion and edge effects. Further the poor adhesion of the encapsulating or encasing materials on the wire or the filament both with glass and also with epoxy resin leads to forcing of fluid under the insulating layer. Also epoxy resins have a poor stability relative to organic solvents, since the components of the resin can be dissolved away. This leads to degradation or altering the epoxy resin. All these effects lead to an increase of the residual current and thus to an increase of the double layer capacitance of the insulating material. Consequently the signal/noise ratio is very unsatisfactory which also affects the response time and the reproducibility of the measurement. Further such ultramicroelectrodes are made by hand, which is connected with high wastage, poor reproducibility and reduced production rate.